Isosceles Triangle Perimeter Formula
The isosceles triangle perimeter formula is used to find the perimeter of an isosceles triangle easily. For an isosceles triangle, the length of only two sides is equal and the measure of corresponding opposite angles is also equal. Let us learn more about the isosceles triangle perimeter formula using the solved examples.
What Is An Isosceles Triangle Perimeter Formula?
For an isosceles triangle of side length a, a, and b respectively, the formula for the perimeter is:
Perimeter(P) = 2a + b
Solved Examples using Isosceles Triangle Perimeter Formula

Example 1: Find the perimeter of the triangle QPR, if the lengths of the sides of the triangle are 8 in, 8 in, and 12 in respectively.
Solution:
Given, a = 8, b = 12Using isosceles triangle perimeter formula,
P = 2a + b
\(P = 2 \times 8 + 12 \)
P = 16 + 12
P = 28Answer: Therefore, the perimeter of the triangle is 28 in.

Example 2: If the perimeter of an isosceles triangle is 160 ft and the length of the third(unequal) side is 30 ft. Find the length of the remaining two equal sides.
Solution:
Using isosceles triangle perimeter formula,
P = 2a + b
\(160 = 2 \times a + 30 \)
\(160  30 = 2 \times a \)
a = 65Answer: Therefore, the length of the equal sides is 65 ft each.